Layer 1 protocols and technologies have evolved including Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy (SDH) in the 1990s to Optical Transport Network (OTN) in the 2000s. SONET/SDH were synchronous protocols optimized for circuit switching and transmission. OTN evolved from SONET/SDH to provide transparency and support for Wavelength Division Multiplexing (WDM) as well as for optimized transmission of packet traffic. SONET, SDH, and OTN each have a rich suite of Operations, Administration, and Maintenance (OAM) functions and support for a wide range of services and applications. Conventionally, as OTN scales beyond 100 G (B100 G), there are emerging frameworks for Layer 1 functionality, namely Flexible OTN (FlexO or B100 G) initiatives in the International Telecommunication Union (ITU) and Flex Ethernet in the Optical Internetworking Forum (OIF).
Traditionally, Ethernet rates were defined in steps of 10×, i.e., 10 Mb/s, 100 Mb/s, 1 Gb/s (GbE), etc. There is a wrinkle in this 10× progression where 40 Gb/s Ethernet (40 GbE) was defined. Today, there are various Ethernet rates defined, including rates in-between established rates. IEEE 802.3 standards group is discussing 2.5 Gb/s, 5 Gb/s, 25 Gb/s and other various odd rates. Specifically, different rates are established for different applications, such as wireless applications, data center group applications, data center interconnections, etc. There is an expectation that different Ethernet rates will continue as new high-volume applications require optimized solutions. Specifically, router/switch equipment and optical transmission equipment are evolving at different rates. There is a desire to support simple transport of n×Ethernet streams across a faster interface. IEEE historically defines Ethernet rates (Media Access Control (MAC) layer) with projects that also define the Physical (PHY)/Physical Medium Dependent (PMD) rates; the MAC rates and PMD rates are tied and defined together. To address evolution in Ethernet and dissociate the MAC/client rate to the PHY/PMD, Flexible Ethernet has been proposed. Note, as described herein, the terms Flexible Ethernet, Flex Ethernet, and FlexE can be used interchangeably.
In transport applications, FlexE can be used to match the flexibility of optical transmission equipment. Specifically, optical transmission equipment (e.g., Dense Wave Division Multiplexing (DWDM)) is evolving to support variable modulation formats, Forward Error Correction (FEC) schemes, baud rates, etc. DWDM equipment can support a variable line rate with the same hardware, to match the data rate to the link capacity. FlexE is based on Ethernet constructs, e.g., 64 b/66 b encoding, recognizing the primary client being transported is Ethernet. Note, the current scope of FlexE, as described in Implementation Agreement IA #OIF-FLEXE-01.0 “Flex Ethernet Implementation Agreement” (March 2016), the contents of which are incorporated by reference, is limited to interfacing applications (e.g., bonding, subrating, and channelization).
Ethernet interfaces are typically defined for Bit Error Rates (BER) of 10−12 and these interfaces address optical reaches of about 70 m to 40 km. There is often a requirement for improved BER targets, such as 10−15, which is more in line to expectations for transport equipment. Ethernet conventionally provides Physical Coding Sublayer (PCS) FEC (e.g., in IEEE 802.3bj, 802.3bs, etc.). However, each time the FEC or reach objective changes, IEEE has to define a new interface, i.e., IEEE 802.3xx. Disadvantageously, new interfaces/specifications impact vendors, operators, and component suppliers.
It would be advantageous to incorporate flexible FEC schemes within existing Ethernet interfaces, avoiding the need for new interface specification and allowing application flexibility.